(This is part five of the chronicle of my Retrochallenge 2015/01 submission, which is to port the modern-day Apple II game, Structris, to the Atari 8-bit home computer using an obscure language called PL65. The mediocrity starts here.)
Only a minor difference in this version versus the previous. Now for each completed row, the pile of pieces will collapse. I was surprised that it didn’t take much additional code in the scroll routine to implement. The algorithm scans the pixels along the bottom of the well. If no $00 (background) pixels are found then the scroll routine performs the “copy pixel from above” from the bottom of the pile (and up) instead of the top of the pile (and up).
Common sense should have me working some easy wins to see this game nearly functionally equivalent to its Apple II hero. This would be keeping track of the rows completed and advancing to the next level. Instead I’m consumed with trying to convert the scroll routine from PL65 to 6502 assembly, for which I have no skill. But then again, common sense should have me working on something entirely different.